pen: Add support for tangential pressure axis.

include/SDL3/SDL_pen.h

@@ -99,6 +99,7 @@ typedef enum SDL_PenAxis
     SDL_PEN_AXIS_DISTANCE,  /**< Pen distance to drawing surface.  Unidirectional: 0.0 to 1.0 */
     SDL_PEN_AXIS_ROTATION,  /**< Pen barrel rotation.  Bidirectional: -180 to 179.9 (clockwise, 0 is facing up, -180.0 is facing down). */
     SDL_PEN_AXIS_SLIDER,    /**< Pen finger wheel or slider (e.g., Airbrush Pen).  Unidirectional: 0 to 1.0 */
+    SDL_PEN_AXIS_TANGENTIAL_PRESSURE,    /**< Pressure from squeezing the pen ("barrel pressure"). */
     SDL_PEN_NUM_AXES        /**< Total known pen axis types in this version of SDL. This number may grow in future releases! */
 } SDL_PenAxis;
 

src/events/SDL_events.c

@@ -378,7 +378,7 @@ static void SDLCALL SDL_EventLoggingChanged(void *userdata, const char *name, co
 
 static void SDL_LogEvent(const SDL_Event *event)
 {
-    static const char *pen_axisnames[] = { "PRESSURE", "XTILT", "YTILT", "DISTANCE", "ROTATION", "SLIDER" };
+    static const char *pen_axisnames[] = { "PRESSURE", "XTILT", "YTILT", "DISTANCE", "ROTATION", "SLIDER", "TANGENTIAL_PRESSURE" };
     SDL_COMPILE_TIME_ASSERT(pen_axisnames_array_matches, SDL_arraysize(pen_axisnames) == SDL_PEN_NUM_AXES);
 
     char name[64];

src/events/SDL_pen_c.h

@@ -34,7 +34,8 @@ typedef Uint32 SDL_PenCapabilityFlags;
 #define SDL_PEN_CAPABILITY_DISTANCE  (1u << 3)  /**< Provides distance to drawing tablet on SDL_PEN_AXIS_DISTANCE. */
 #define SDL_PEN_CAPABILITY_ROTATION  (1u << 4)  /**< Provides barrel rotation info on SDL_PEN_AXIS_ROTATION. */
 #define SDL_PEN_CAPABILITY_SLIDER    (1u << 5)  /**< Provides slider/finger wheel/etc on SDL_PEN_AXIS_SLIDER. */
-#define SDL_PEN_CAPABILITY_ERASER    (1u << 6)  /**< Pen also has an eraser tip. */
+#define SDL_PEN_CAPABILITY_TANGENTIAL_PRESSURE (1u << 6)  /**< Provides barrel pressure on SDL_PEN_AXIS_TANGENTIAL_PRESSURE. */
+#define SDL_PEN_CAPABILITY_ERASER    (1u << 7)  /**< Pen also has an eraser tip. */
 
 typedef enum SDL_PenSubtype
 {

src/video/cocoa/SDL_cocoapen.m

@@ -89,10 +89,10 @@ static void Cocoa_HandlePenProximityEvent(SDL_CocoaWindowData *_data, NSEvent *e
             return;  // oh well.
         }
 
-        // Cocoa offers almost none of this information.
+        // Cocoa offers almost none of this information as specifics, but can without warning offer any of these specific things.
         SDL_PenInfo peninfo;
         SDL_zero(peninfo);
-        peninfo.capabilities = SDL_PEN_CAPABILITY_PRESSURE | SDL_PEN_CAPABILITY_ROTATION | SDL_PEN_CAPABILITY_XTILT | SDL_PEN_CAPABILITY_YTILT | (is_eraser ? SDL_PEN_CAPABILITY_ERASER : 0);
+        peninfo.capabilities = SDL_PEN_CAPABILITY_PRESSURE | SDL_PEN_CAPABILITY_ROTATION | SDL_PEN_CAPABILITY_XTILT | SDL_PEN_CAPABILITY_YTILT | SDL_PEN_CAPABILITY_TANGENTIAL_PRESSURE | (is_eraser ? SDL_PEN_CAPABILITY_ERASER : 0);
         peninfo.max_tilt = 90.0f;
         peninfo.num_buttons = 2;
         peninfo.subtype = is_eraser ? SDL_PEN_TYPE_ERASER : SDL_PEN_TYPE_PEN;
@@ -136,6 +136,7 @@ static void Cocoa_HandlePenPointEvent(SDL_CocoaWindowData *_data, NSEvent *event
     SDL_SendPenAxis(timestamp, pen, window, SDL_PEN_AXIS_ROTATION, [event rotation]);
     SDL_SendPenAxis(timestamp, pen, window, SDL_PEN_AXIS_XTILT, ((float) tilt.x) * 90.0f);
     SDL_SendPenAxis(timestamp, pen, window, SDL_PEN_AXIS_YTILT, ((float) tilt.y) * 90.0f);
+    SDL_SendPenAxis(timestamp, pen, window, SDL_PEN_AXIS_TANGENTIAL_PRESSURE, event.tangentialPressure);
 }
 
 SDL_bool Cocoa_HandlePenEvent(SDL_CocoaWindowData *_data, NSEvent *event)